The pilot study on which this proposal is based has shown that alternative configurations of the optic nerve and Mauthner cell axon decussations of goldfish (Carassius auratus) have different behavioral manifestations. Preliminary evidence suggests that the geometry of these decussations--i.e., whether the dorsal component of a decussation is contributed by the right or left side of the nervous system--is related to lateral asymmetries in size of neural structures from which the decussating axons originate. To test a hypothetical causal sequence in the development and behavioral manifestations of lateral asymmetries in goldfish, the following strategies will be employed: (1) 3H-thymidine autoradiography and careful measurements of the developing nervous system will be used to determine whether there are consistent lateral asymmetries in cell cycle dynamics or in the allocation of neural plate materials. (2) A combination of Bodian staining for normal nerve fibers and horseradish peroxidase or cobalt neuronography of geometrically complex decussations will be used to test the generality within the goldfish nervous system of the decussation patterning characteristics exhibited by the optic and Mauthner cell chiasmata. (3) Behavioral profiles of individual fish, including orientation and position preferences, optomotor behavior and characteristics of startle responses will be correlated with the longitudinal distribution of lateral asymmetries.